With popularization of a mobile telephone, a personal digital assistance (PDA), and the like, display panels each of which has a high-definition image display function and can realize a small thickness and a low power consumption are increasingly demanded. Conventional liquid crystal display panels have been employed in various products including the products described above as display panels which fulfil the demand.
On the other hand, in recent years, a display panel using an organic EL (electroluminescence) elements which take advantage of being light-emitting elements as light-emitting pixels is realized. The display panel attracts attention as a next-generation display panel replaced with a conventional liquid crystal display panel. By using an organic compound which can expect a preferable light-emitting characteristic on a light-emitting layer of the element, practical high efficiency and long life are advanced in the background.
In addition to the display panel, a personal digital assistance having a touch sensing function which, in response to display information displayed on the display panel, touches a display screen of the display information by using a fingertip, a touch pen, or the like to make it possible to input various commands is also proposed. This can be preferably employed in the PDA or the like.
The conventional display apparatus including the touch sensing function realizes its integration such that a touch panel having a touch sensing function and an EL display panel are manufactured as independent parts, and the touch panel is stuck to a surface of the display panel. This is described in Patent Document 1.
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-156920
As described in the Patent Document 1, the display panel and the touch panel are integrated with each other by being stuck to each other to cause a problem of an increase in entire panel thickness. The display apparatus cannot meet the demands of thinning and miniaturization made by the personal digital assistance which is very strongly demanded to be thinned and miniaturized.
When a film-like resistive film touch panel is used as described in the Patent Document 1, a transmittance of light from the display panel decreases because a transparent electrode (ITO film) is formed on the panel surface, and the touch panel surface is colored by the transparent electrode to disadvantageously cause a color shift (deviation) on a display image.
In order to solve the above problems, an SAW touch sensing function which does not need to form a transparent electrode for a touch sensing function as described on the Patent Document 1 on a panel surface is employed, and without using a configuration in which a touch panel is stuck to a display panel as described above, the SAW touch sensing function is formed on the other surface of the transparent substrate on which an organic EL element is formed is proposed. The configuration is disclosed in the following Patent Document 2, Patent Document 3, and the like.
Patent Document 2: Japanese Patent Application Laid-Open No. 2002-366303
Patent Document 3: Japanese Patent Application Laid-Open No. 2003-036144